This invention relates to plasma reactor chambers and, in particular, to a plasma reactor chamber having a slotted manifold plate.
Plasma processing is finding increasing use in the semiconductor industry, not only for "ashing" or the removal of photoresist but also for the highly selective etching of a variety of layers. Further, plasma processing can be used for depositing layers as well.
As these processes become more widely used and as the dimensional requirements of semiconductor devices become smaller and smaller, uniformity across the wafer becomes a critical factor in determining yield. Further, there must be uniformity or reproducibility from wafer to wafer.
In the past, uniformity has been improved, as disclosed in U.S Pat. No. 4,209,357, by providing a gas manifold having a plurality of apertures located across the face thereof for supplying the reactive gas or gas mixture at a plurality of sites across the surface of the wafer. In addition, a plurality of vacuum ports are provided for exhausting reaction products from the chamber.
In this arrangement, supply and exhaust apertures alternated across the surface of the chamber in somewhat of a checkerboard pattern. While improving the availability of active species for reaction at the surface of the wafer, the flow of gases through the apertures formed a plurality of jets, so that pressures and flows had to be carefully adjusted to avoid a waffle-shaped reaction pattern.
An alternative to this is to provide what is known as a radial flow plasma reactor. In this configuration, reactive gases are supplied through a plurality of apertures in the central regions of the reactor, while gases are exhausted through an annular exhaust port which surrounds the gas supply apertures. In this configuration, the flow of gases is sufficiently non-uniform that the reaction is non-uniform. In particular, gases at the central region of the wafer are relatively stagnant compared to gases at the edge of the wafer, adjacent the exhaust port. As a result, active species are more readily depleted at the center than at the edge.
To a large extent, this problem and the preceding problem can be obviated by the careful choice of pressure, gas flow, and applied RF power. Unfortunately, this is more true for smaller wafers than for larger wafers, e.g. wafers having a diameter or largest dimension of 125 mm. or greater.
In view of the foregoing, it is therefore an object of the present invention to provide a plasma reactor having improved uniformity of gas delivery and exhaust.
It is another object of the present invention to provide a gas manifold plate having reduced resistance to gas flow.
It is a further object of the present invention to provide a gas manifold for a plasma reactor having low gas velocity adjacent the manifold.